1. Field of the Invention
This invention relates generally to spinal implant systems, and more particularly, to a mobile sleeve structure that maintains a determinable spatial relationship between adjacent vertebrae.
2. Description of the Related Art
There is a need in the field of neurosurgery for spinal implant systems that enable surgeons to maintain a determinable spatial relationship between adjacent vertebrae during vertebral fusion procedures. A typical vertebral fusion procedure involves implanting a bone graft or cage element into the intervertebral region known that normally would be occupied by a disc. Patients that suffer from degenerative disc disorders may be required to undergo a surgical procedure that involves the fusing together of the adjacent vertebrae that are located immediately above and below the disc region. During a vertebral fusion procedure, bone grafts are inserted into the disc region to facilitate fusion of the vertebrae by promoting growth of bone in the disc. The result is that the vertebrae will eventually fuse together. Such patients may additionally require a series of such bone grafts that will result in the fusing together of several vertebrae in the cervical vertebral column.
A problem with vertebral fusion procedures is that once the bone grafts are implanted they are prone to becoming misplace due to movement of the adjacent vertebrae. In response to this problem several systems have been developed that will immobilize the adjacent vertebrae by attaching a plate between the adjacent vertebrae. The attached plate will maintain the spatial relationship between the vertebrae and promote fusion by preventing slippage of the bone grafts during the fusion process.
One known system for maintaining spinal elements in a desired spatial relationship incorporates a series of plates having predetermined heights and shapes. Each such plate has a plurality of apertures disposed at lengthwise distal ends of the plate. Bone screws are threaded through the apertures to attach the plate to a corresponding one of a pair of anterior cervical vertebrae. The plates so attached maintain a spatial relationship between the two adjacent vertebrae that are located immediately above and below a bone graft implant. In the known system, the plates are attached to extend longitudinally with respect to the axis of an anterior cervical vertebral column.
It is a deficiency of the above system that plates of various heights must be prefabricated and made available during the procedure because the distance between respective pairs of vertebrae will vary along the length of the anterior cervical column. Thus, upon the conclusion of the procedure there will remain several unused plates that will have to be disposed of or sterilized.
Another problem with the known system is that the plates are only used between two vertebrae and cannot be used to maintain a desired spatial relationship between three or more vertebrae. Three or more vertebrae may need to be secured in predetermined relation to one another when the patient is diagnosed to require more than one bone graft implant. Some systems have been developed that use a one-piece rod that can be attached across several vertebrae. A problem with the known rod system is that it does not accommodate the natural lordotic curvature of an individual patient's spinal column as the lordotic curvature varies from patient to patient.